Underground line question

First of all, I plan on finding a foam contractor and having my lines foamed in the ground. In a recent similar thread, someone mentioned running their underground PEX inside of black drain pipe and then foaming that in place just in case they needed to ever replace the lines, add more, or to ensure there will be 0 water infiltration if the closed cell foam ever does get waterlogged. I thought that was a great idea, but realized it would make more sense to run separate drain lines to run the PEX inside so you're not transferring heat between your supply and return lines if they are run together.

So I just did a little pricing of parts. My trench is going to be about 100' long. 250' of 4" drain tile is about $100. Foaming 4x8" of tile into the ground with 2-3" all around it would use quite a bit of foam and require one heck of a trench too. But, 10' sections of 2" plastic electrical conduit is a little less than $4 each. For 200' (supply and return) of that is about $80. I can seal 10' sections of the conduit with PVC glue to keep them watertight, although it really isn't necessary since the foam should keep the water out 100%. 2x4" of piping to foam 2-3" over requires a lot less foam as well. Plus, should I ever have the need to replace the PEX, the electrical conduit will be much more slippery than the drain tile for sliding 100' of tubing through. Although the electrical conduit is "rigid," it will still be fairly flexible. Another great plus is that I plan on pouring my concrete pad today and to get the lines from underground and up through the pad, I was already planning on using the large electrical conduit elbows because of their large radius curve which will make a nice gentle turn for the PEX. I'm going to do 2 2" elbows for the PEX and 2 1" elbows for electrical and control wires. I might add a couple elbows with nothing to go through them just in case I ever need to use them.


So here's my question:
I'm going to be using 1-1/4" PEX. I realize that size is pretty much the OD of the PEX. will 1-1/4" PEX slip through 2" conduit OK? I don't know what the ID of 2" conduit actually is.

woodsmaster said:

The I.D. of 2" conduit is 2" My 1 1/4 pex is 1 1/4" I.D. It is thermopex. The O.D. of the 1 1/4 pex is 1 1/2"

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So with that 1/2" of play, there shouldn't be any problem sliding the PEX through the conduit?

I went to Lowes. I tried 1" PEX through the 2" elbow. It was a PITA, but it went through. I tried 1-1/4" black plastic pipe (since Lowes doesn't carry 1-1/4" PEX) and I couldn't get it through. It was nearly impossible to get it through the 3" conduit elbow. I ended up buying two 100' rolls of 3" drain pipe for $96, although I'm not too happy with that idea. I could slide the conduit sections onto the PEX as I install it. It's not too late to go back and buy 2" elbows still and return this stupid drain tile. Do you think if I set the PEX in the 90+ degree sun for a couple hours, it would soften up enough to stick through the 2" elbow? I'd much rather have that than drain pipe.

Just got in from setting up my concrete forms. I'm going to return the drain pipe tomorrow and pick up 2" PVC conduit. I was trying the plastic pipe inside of the sweeping 90's, but I do think a little heat will make it go through just fine. I'm going to slip the sections on one at a time as I lay the PEX.

Alright, the pads are poured. Because I was running short on time and some pesky roots were making my digging a PITA, I opted to build a little boxed area that did not receive concrete as originally suggested by the manufacturer of my furnace. After it's cured, I'll then dig under that part of the pad, run the conduit up through, put the dirt back in place, and then fill in the boxed area of concrete with a hand mixed bag of concrete. Then I'll finally set the furnace on the pad.

The pour went well. I ordered one yard delivered and that was about the perfect amount of concrete. We only ended up throwing about 2 shovels full out of the frame while we were working. I purposefully poured the pad 6" thick and I wire screened it using chunks of brick to hold the screen about 2" off of the ground as we poured. This pad should last a while.

Pictures once it's a couple days dry.

Since the PVC would not actually be carrying any fluid, I'm not worried about expansion and contraction.

I do wonder if I could bend my own 2" PVC conduit. That would be pretty cool. I bet I could make a heating blanket of sorts.



Just a curious wondering at this point...old 1-3/4" fire hose is free to come by. Is there any reason I couldn't sleeve the PEX inside of that? I can get 100' lengths of the stuff and it's obviously very flexible. It shouldn't degrade encased inside of the foam. The only benefit I'd lose is the ability to replace the PEX just by sliding the old out and the new in.

in hot water said:

The sleeve need to be 100% water proof and able to withstand some temperature, especially encased in foam. I'm not sure fire hose fits all those requirements.

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It's fire hose. By definition it's waterproof and routinely withstands temperatures well above 200 degrees.


Are you guys sure other kinds of PVC are going to be cheaper than $.40/ft? I'm not finding it anywhere, so where are you?

Extra security in case the foam ever become waterlogged? Maybe it's not worth the effort...